You probably have the notorious Bendix 10 ABS system. Go to:
http://www-odi.nhtsa.dot.gov/cars/problems/recalls/recallsearch.cfm
Search using campaign recall 96V099000 (which is Chrysler recall #685) click
on the "Document Search" link and read all the info. Good luck.

Hmmm...there was a 'recall' on the ABS system for 92-94, IIRC. One of the
modules goes awry and causes the symptoms you're describing. There is a
guy in alt.auto.dodge that can tell you more about this, his 'name' is
maxpower. IIRC, the recall goes up to 100,000, so if you haven't passed
this magic mark yet, get thee to a dealer!

However, maxpower also told me I was up the river without a paddle, since
I had 130,000 miles (he works at a dealer) and that I would have to
replace a $600 module. They are readily available at junkyards, but in
some states, brake parts can't (or aren't *supposed* to) be sold from
junkyards.

So, I asked about flushing and refilling the brake system with fresh
fluid. Max asked me if I was nuts and wanted to take the risk on brake
failure for $12 worth of brake fluid.

Well, I was doing all the brakes on the van and since I was at it, I
flushed the brake fluid (start at the pass side rear, then the driver's
side rear, then the pass front and finish with the driver's front).
Guess what? Worked. Pedal pressure came back to normal and never faaded
for the rest of the time I owned the van (about another 4 months,
unfortunately...).

Since this takes a Saturday afternoon and $12-15 worth of brake fluid, I
would give it a try. Let me know if you want to attempt this, and I'll
give you some more detailed instructions...

There is supposedly some 'special' method for flushing and bleeding on
these, but like I said, it worked great. If you're lesas than confident
you may want to take it to a dealer.  Or. google it. The instructions are
out there.